This invention relates to (a) novel processes for controlling the evaporating of liquid from a chemical sample, with drying gas, or like processes, and (b) apparatus useful in such processes.
It is often desirable to transfer a solute from one solvent system to another solvent system. For example, this procedure is used frequently in liquid chromatography where a first solution, perhaps a liquid fraction obtained from one chromatographic procedure, can be more specifically analyzed by use of a different solvent to carry the dissolved components of the first solution. In the past, it has been common to place the first solution into a tube and, using a gas sparge tube, or cannula, contact the solution with sufficient drying gas to remove the unwanted liquid.
A number of problems are associated with this procedure. Sometimes a sensitive solid product is damaged by continuing to pass drying gas into the apparatus beyond the optimum drying point. Moreover, it is sometimes desirable to leave the solid contents in a somewhat pasty or damp condition. At present, to avoid damage of such samples, it is convenient to dry stepwise or to slow down drying rate to a fraction of the possible drying rate, thereby reducing the chance that an operator will be inattentive for a period long enough to allow the samples to be dried excessively.